As the topic says, the link to [[Special:ParserDiffTest]] from [[Special:Version]] is broken. It's currently pointing to [[Special:ParserDiffTestSpecial]], which doesn't exist. I don't see any wikicode in the $wgExtensionCredits for it though, so I can't submit a diff.
(Wanted to submit under extensions, but there wasn't an applicable entry, sorry if it ended up miscategorized)